Abstract: Peutz-Jeghers syndrome (PJS) is a rare hereditary multiple polyposis syndrome associated with a high risk of both gastrointestinal and non-gastrointestinal epithelial malignancies. However, few studies have been reported on the use of ¹⁸F-fluorodeoxyglucose (FDG) PET/CT in these patients. Herein, the authors report a case of PJS complicated by pulmonary invasive mucinous adenocarcinoma. The clinical manifestations, genetic features, as well as CT and ¹⁸F-FDG PET/CT findings are presented to discuss the diagnosis of this condition.